TheSamba.com :: View topic - How do I know if my bus is charging my battery?

Mon Nov 09, 2009 6:36 pm

That's about the extent of it - can I measure if my battery is being charged when my bus is running?

Thanks, don

Mon Nov 09, 2009 6:38 pm

Yes...measure across the battery terminals with your DVOM with the Bus off and you should get about 12.5 volts or so. Start it up and you should be around 14.5....or just look at the dash and see that the battery light is off while the Bus is running.

Mon Nov 09, 2009 7:12 pm

^ Agreed

Use a volt meter to know for sure, but that's also what the "idiot lights" are for. With your key in the ON position (engine not running), do you get a charge light in the dash (looks like a little battery, or a circle with a G in it for earlier models)? If so, that verifies that the bulb is working. Now start the engine - if that light goes out... then you're charging. If the light stays on, you're not charging. If the light never came on to begin with, then you don't know what's going on because the bulb and/or connection is no good, fix the bulb and try again, and in that case you should verify with a meter also.

Mon Nov 09, 2009 7:15 pm

Daverham wrote: If the light never came on to begin with, then you don't know what's going on because the bulb and/or connection is no good

Not entirely true Dave......if the battery light isn't coming on at all in a late Bus I can tell you 100% that the battery isn't being charged. The idiot light is part of the system and if it doesn't work, the alternator doesn't charge. That light absolutely must come on when you turn the key to the "on" position, or you won't charge at all.

Mon Nov 09, 2009 7:23 pm

Really? You're saying that if the bulb burns out, that alone will prevent the battery from charging, even if the rest of the system would otherwise be working properly?

Mon Nov 09, 2009 9:03 pm

Of course you could always install a voltage or amp guage?

cheers........ :roll:

Tue Nov 10, 2009 8:00 am

So it looks like my battery is 12v (was 12.8 when I bought it 2 weeks ago). When I turned the key the indicator light came on on the dash and when the bus was running I saw 13.2v between the terminals. I guess this is a good sign but it seems the battery is slowly loosing it's cranking power.

Thanks all for the advice and I'll keep you posted if I see any changed.

-don

Tue Nov 10, 2009 8:16 am

13.2v is pretty weak, your alternator may be telling you it's on the way out. Clean all the connections between the alternator and starter and alternator and regulator, pay close attention to where the wires enter the crimped on terminals and make sure the plug terminals are staying in the plug and making contact at the regulator terminals.

Daverham, yes, no light at all means no charge, the bulb has to work.

Tue Nov 10, 2009 8:23 am

Are you sure no light means no charge? This sounds wrong. If the light is burnt out or disconnected that should not make the alternator stop charging.

Tue Nov 10, 2009 8:39 am

The system that VW used requires the resistance of the light to supply enough power to excite the alternator. Unlike a generator an alternator needs power to begin charging.

Tue Nov 10, 2009 8:42 am

Nica wrote: Are you sure no light means no charge? This sounds wrong. If the light is burnt out or disconnected that should not make the alternator stop charging.

Yes, the wire going to the field on the alternator is in series with the bulb filament. If the bulb filament breaks then you have no voltage to energize the field and therefore no charge coming from the alternator. I agree that it sounds dumb but that's the way they made them.

Tue Nov 10, 2009 8:42 am

Nica, please believe it. That little warning lamp in the dash has to function when it comes to alternators. Same with generators, but the charging part does not apply, but it will warn you when the fan belt ruptures. Bottom line, no warning light, no good despite the charging system.

Tue Nov 10, 2009 8:46 am

Got it, I'll try to check it out tonight with the flood light. And good to know about the bulb. My dash lights don't work at all and I'd probably have let that light stay out if it when out...

Sure enough when I started my bus this morning it *just barely* cranked the engine over, I decided to take the long way into work onto the freeway to charge it up a bit more (and park on a hill). -don

Tue Nov 10, 2009 8:46 am

... Or read up on the design. Burned out light means no charging.
http://www.nls.net/mp/volks/schem/mot_alt.htm

Tue Nov 10, 2009 2:53 pm

Never knew that. I have learned something for once. What about when the light falls out of its socket on rough roads? I never would have imagined that makes the alternator stop charging as I have simply ignored the disconnected light in the past for a few days.

Tue Nov 10, 2009 2:57 pm

Wait I think I understand now. The wire going to the bulb is in a series, so that's why the wires that go to the light are two small green ones in the engine compartment? So if the light is burnt there is no charge;understandable. But what if it is disconnected?

Tue Nov 10, 2009 2:57 pm

meaning not in her socket.

Tue Nov 10, 2009 2:58 pm

If the idiot light in the dash doesn't light up when you turn the key on, you have no charging. Period. No more what ifs...if you don't have the light on, you don't charge the battery. It can't be any more clear.

Tue Nov 10, 2009 3:04 pm

However, the converse is not always true. The bat light can be on, but the battery can be charging fine.

Last fall, I had a problem whereby my bat light did not light up when the key was turned to on, but when the vehicle was running, the bat light came on steady and bright, yet both of my batteries were charging as normal (they both have voltmeter gauges - 14+ volts). However, my turn signals did not work.

So I spent lots of time reading and searching troubleshooting threads, changed the alt, tested VR, tested the blue wire, etc, and after all was said and done, I still had no resolution. In the end, it turned out to be a blown fuse, number 12.

I drove the bus around like that for about a month (carefully, no turn signals, couple of VW cruises), parked it over winter, and discovered the problem this spring when I did the aforementioned troubleshooting.

Tue Nov 10, 2009 3:21 pm

So you guys are only talking about Bays '72 and later, right? Not applicable to upright engined bays with a generator or those that were converted from generator to alternator, right?